Polymeric web compositions for use in absorbent articles

ABSTRACT

The properties of (meth)acrylic ester/(meth)acrylic acid copolymer webs, such as films and nonwovens, are improved by blending the ester/acid copolymer with polyethylene glycol. The polymer blend provides a polymeric material which is useful for making personal care products such as diapers and feminine pads in that it can be made water-soluble while exhibiting other properties which are necessary for adequate product performance.

This is a divisional application of copending application Ser. No.07/715,944, filed on Jun. 14, 1991, which is a divisional of applicationSer. No. 07/598,276 filed on Oct. 16, 1990, now U.S. Pat. No. 5,063,272.

BACKGROUND OF THE INVENTION

In the production of personal care products, a number of differentcomponents and materials are required to construct the products. In thecase of diaper manufacture, for example, these components include abacking material, which is a film, and an inner liner, which istypically a nonwoven web. Also, composite structures of synthetic andnatural fibers have utility as absorbent media in a variety of personalcare products. These various synthetic components are typically madefrom thermoplastic polymers such as polyethylene or polypropylene.However, with a greater emphasis being placed on protecting theenvironment today, there is a need to develop materials which are morecompatible with existing and developing waste technologies while stilldelivering the performance consumers have come to expect.

Copolymers of (meth)acrylate esters and (meth)acrylic acid are ofenvironmental interest because of their solubility in alkaline solutionsor upon prolonged exposure to moisture, even though they are relativelyhydrophobic. Unfortunately, the physical properties which make thesematerials desirable from an environmental standpoint can make themunsuitable for personal care products. In particular, films made fromthese polymers in contact with synthetic urine for a period greater thanone hour will become hydrated, weak and sticky. This is obviouslyunacceptable for use in diapers, for example. Films made from thesepolymers also suffer from a lack of toughness and tear resistance. Filmsand nonwovens made from these copolymers are somewhat sticky and tend tostick or "block" in roll form. In addition, dimensional stability andaesthetic properties of these materials are also poor. Finally, theviscosity of these polymers in the temperature ranges appropriate forthe production of nonwovens is too high to be compatible with certainnonwoven processes.

Therefore there is a need for copolymers of (meth)acrylate esters and(meth)acrylic acid which have modified properties suitable for use ascomponents in personal care products.

SUMMARY OF THE INVENTION

It has now been found that copolymers of (meth)acrylate esters and/or(meth)acrylic acid can be modified with additional materials to providepolymeric webs having improved properties suitable for use in personalcare products. More specifically, it has been discovered thatpolyethylene glycol, when blended with such ester/acid copolymers,imparts reduced viscosity and increased processability in meltblown andsimilar processes. In addition, the webs produced have a measure ofelasticity and can be stretched with recovery. Furthermore, saidpolymeric webs can be heat treated to induce a reaction between theblended polymers, thus further altering the characteristics of the web.

Hence, in one aspect, the invention resides in a composition of mattercomprising a polymeric blend of from about 60 to about 95 weight percentof a (meth)acrylate ester/(meth)acrylic acid copolymer and from about 5to about 30 weight percent polyethylene glycol.

In another aspect, the invention resides in a polymeric web comprising ablend of from about 60 to about 95 weight percent of a (meth)acrylateester/(meth)acrylic acid copolymer and from about 5 to about 30 weightpercent of a polyethylene glycol. The relative proportions of the twopolymers will depend upon the desired properties of the product intowhich they are to be made. For use in making nonwoven webs, such asmeltblown webs, it is preferred that the copolymer blend contain fromabout 70 to about 90 weight percent of the ethyl acrylate/methacrylicacid copolymer and from about 5 to about 20 weight percent of thepolyethylene glycol.

In a further aspect, the invention resides in an absorbent articlehaving an outer cover, an absorbent core, and an inner liner, whereinsaid absorbent core comprises a composite structure including apolymeric web as described herein. Suitable absorbent articlesparticularly include diapers and sanitary napkins.

The ethyl acrylate/methacrylic acid copolymer that is most preferred hasa 4:1 ratio of the two comonomers by weight. The weight averagemolecular weight is about 150,000, with a melt flow rate of about 7grams per 10 minutes, as measured at 170° C. using a 2160 g weight and a2.1 mm by 8 mm capillary. Clearly, however, many similar copolymers canbe prepared that will provide similar attributes and can be substitutedfor the most preferred copolymer in these compositions. For example, anyother (meth)acrylate ester derived from an alcohol having from 1 to 18carbon atoms can be substituted for all or part of the ethyl acrylate.Such substitutions can lead to enhancement of particular properties forspecific material applications. The manufacture of such copolymers isdescribed in U.S. Pat. No. 4,870,148 to RB KunststoffpatentVerwertugs AGand Belland AG, both of Switzerland, issued Sep. 26, 1989, which isherein incorporated by reference. Such copolymers are commerciallyavailable from Belland AG, and the most preferred copolymer is availableas product code "GBC 2630".

Suitable polyethylene glycols are available commercially from UnionCarbide Corporation, Tarrytown, New Jersey, under the tradenameCARBOWAX®; most suitable are product code numbers "3350" and "8000."

Blends of the two polymers can be prepared by mixing the desired weightratio of the polymer pellets and blending them using any standardequipment commonly used for blending thermoplastic polymers underconditions of heat and high shear. These include the Banbury® type ofintensive production mixer (Farrel Corp. Ansonia, CT) and both single-and twin-screw compounding extruders, which can utilize high-shearmixing screws, co-rotating kneading blocks, etc.

Processing characteristics of the polymer blends described herein can bemodified by the incorporation of lubricants or slip agents into theblends. Additives of other types normally used in polymer blends canalso be incorporated to provide specific properties as needed, such asantistatic agents, pigments or other colorants, and the like. Each ofthese additive types are generally used in small amounts, usually about5 percent or less.

Nonwoven webs of the two polymers can be prepared by extrusion of theblend through a plurality of capillaries, producing a series offilaments. These filaments can be quenched and attenuated into fibers byan accelerating gas stream. The fibers can be collected on a movingsurface, where they are deposited by the gas stream in a random fashion.Passing the resulting batt through a pair of heated roll bonds thefibers together into an integral web. Alternatively, a hot gas streammay be used to attenuate and break the filaments in the molten state.These discontinuous fibers can be collected on a moving surface, wherethey will lay down in a random, entangled manner, producing an integralweb. Suitable nonwoven webs include, without limitation, meltblown webs,spunbonded webs, and coform webs (meltblown webs in which a second fibersource, such as cellulose fibers, is blown into the primary meltblownfiber stream prior to deposition onto the collecting surface). All ofsuch webs are known in the nonwovens art.

EXAMPLE Preparation of Polymer Blend and Nonwoven Web

A copolymer blend containing 80% GBC 2630 AA (a 4.3:1 ethylacrylate/methacrylic acid copolymer with no additives), and 20%CARBOWAX® 3350 (Union Carbide, polyethylene glycol of molecular weight3000 - 3700) was prepared using a 3/4" single-screw compounding extruderwith a single mixing section and L/D of 26:1. Strands were generatedthrough a dual-strand die at 160° C., allowed to air cool, andpelletized.

Intrinsic viscosity of this blend was measured using a capillaryrheometer with a capillary diameter of 0.0202 inches and L/D ratio of4.89. The viscosity of the blend was 410 poise at 170° C. and 1075 s⁻¹.The unblended ethyl acrylate/methacrylic acid copolymer had a viscosityof 1178 poise under the same conditions. It was found that the blendedpolymers increased in viscosity over time when heated to 400° F.,apparently due to a reaction in which the poly(ethylene glycol) graftsto the ethyl acrylate/methacrylic acid copolymer.

This blend was processed through a heated piston apparatus to force themolten blend through a 1 mm orifice at a temperature of 385° F. Thefilament formed was attenuated using hot air and deposited randomly on amoving collection wire, forming a web with some integrity. This polymerblend and forming method can be used to product composite structures(coforms) suitable for a variety of personal care absorbent products.The composite is soluble and dispersible on immersion in a basicsolution.

It will be appreciated by those skilled in the art that the foregoingexample, given for purposes of illustration, is not to be construed aslimiting the scope of this invention.

I claim:
 1. An absorbent article having an outer cover, an absorbentcore and an inner liner, wherein said absorbent core comprises acomposite structure comprising a polymeric web comprising a blend offrom about 60 to about 95 weight percent of a copolymer of a(meth)acrylate ester and (meth)acrylic acid and from about 5 to about 30weight percent of polyethylene glycol.
 2. The absorbent article of claim1 wherein the absorbent article is a diaper.
 3. The absorbent article ofclaim 1 wherein the absorbent article is a sanitary napkin.
 4. Theabsorbent article of claim 1 wherein the (meth)acrylate ester is ethylacrylate.
 5. The absorbent article of claim 4 wherein (meth)acrylic acidis methacrylic acid.
 6. The absorbent article of claim 5 wherein thecopolymer of ethyl acrylate and methacrylic acid comprises about 80weight percent ethyl acrylate moieties and about 20 weight percentmethacrylic acid moieties.
 7. The absorbent article of claim 5comprising from about 70 to about 90 weight percent of a copolymer ofethyl acrylate and methacrylic acid and from about 5 to about 30 weightpercent of polyethylene glycol.
 8. The absorbent article of claim 7wherein the amount of polyethylene glycol is from about 5 to about 20weight percent.
 9. The absorbent article of claim 5 wherein thepolymeric web comprises a blend of about 80 weight percent of acopolymer of ethyl acrylate and a methacrylic acid and about 20 weightpercent polyethylene glycol.